1. Field of the Invention
The present invention relates generally to thermoplastic composite materials and more particularly to a thermoplastic multi-layer composite structure.
2. Description of the Prior Art
Thermoplastic composite materials are well known and used in various industries including the marine industry. Recently, with the movement towards improving the environment, several regulations, treaties and laws have been passed to help protect the environment.
Currently, in the marine industry, as well as numerous other industries, the use of fiberglass as a construction material is highly prevalent. Fiberglass is defined as a material consisting of extremely fine filaments of glass which can be embedded in various resins to make boat hulls, fishing rods, and the like. The fine filaments of glass can also be combined in yarn and woven into fabrics or used in masses as a thermal and acoustical insulator. Fiberglass wool, a thick, fluffy material made from discontinuous fibers, is used for thermal insulation and sound absorption. The fiberglass wool is often found in ship and submarine bulkheads and hulls, as well as automobile engine compartments and body panel liners.
The major ingredients of fiberglass include silica sand, limestone, and soda ash. The silica sand is used as the glass former, and the limestone and soda ash are provided primarily to lower the melting temperatures. Other ingredients can also be utilized and are usually provided to improve certain properties such as chemical resistance. When creating fiberglass the raw materials are carefully weighted in exact quantities and thoroughly mixed together before being melted into glass.
Once prepared, the mixed materials are fed into a furnace for melting. The temperature of the furnace is precisely controlled to assure a smooth, steady flow of glass. To form into fiber, the molten glass is kept at a temperature of approximately twenty-five hundred (2500xc2x0 F.) degrees fahrenheit. Once the glass becomes molten, it is transferred by a channel disposed at the end of the furnace to the forming equipment.
The type of fiber desired determines which process is utilized to form the fiber. Textile fibers can be formed from the molten glass directly from the furnace. Alternatively, the molten glass can be fed first to a machine that forms glass marbles which can be inspected visually for impurities. The glass or glass marbles are then fed through spinnerets which are heated bushings, to allow the molten glass to pass through its numerous orifices and come out as fine filaments.
To produce a long, continuous fiber, multiple strands of the glass which passes through the orifices of the spinneret, are caught up on a high-speed winder. The winder revolves at a much faster rate that the rate of flow of the molten glass out of the orifices. The tension pulls out the filaments while still molten, to form strands a fraction of the diameter of the orifices. A chemical binder can be applied to help prevent the fibers from breaking. The filaments are then wound upon tubes where they can be twisted and plied into yarn.
Another process in known as the staple-fiber process wherein as the molten glass flows through the bushing, jets of air rapidly cool the filaments. The air also breaks the filaments into certain lengths. The broken filaments fall through a spray of lubricant onto a revolving drum, where they form a thin web. The web is pulled from the drum and sent into a continuous strand of loosely assembled fibers. The strand can then be made into yarn as described above.
Instead of forming the filaments into yarn, the strands may be chopped into short lengths. The chopped fiber is formed into mats and a binder is provided. After curing in an oven, the mat is rolled up.
To make a glass wool, the molten glass flows from the furnace into a rapidly spinning cylindrical container having small holes. The spinning of the container, allows horizontal streams of glass to flow out of the holes. The streams of molten glass are converted into fibers by a downward blast of air or hot gas. The fibers fall onto a conveyor belt, where they interlace with each other in a fleecy mass which can be used as insulation. Alternatively, the wool can be sprayed with a binder, compressed to a desired thickness and cured in an oven. The heat from the oven fixes the binder, and the end product may be a rigid or semi-rigid board.
In addition to binders, other coatings may also be required for fiberglass products. For example, lubricants can be utilized to reduce fiber abrasion. The lubricant is directly sprayed on the fiber or added into the binder. Furthermore, an anti-static composition can be sprayed onto the surface of fiberglass insulation mats during cooling. The anti-static composition usually is provided to minimize static electricity and to act as corrosion inhibitor and stabilizer. Additionally, coupling agents can be provided on the strands, when the strands are utilized for reinforcing plastics, to strengthen the bond to the reinforced material.
As seen from the above description, the manufacture of products using fiberglass as a primary component is relatively expensive and labor intensive. Furthermore, fiberglass does not have good energy absorbing characteristics, which causes nearly all of the impact forces to be translated through the fiberglass.
Furthermore, where a boat is constructed from wood or fiberglass, virtually all of the wave slap energy or wave impact energy from the bottom of the boat is translated through to the deck where the driver and/or passengers are positioned. Thus, hardly any, if any, of the energy from the waves is absorbed by the fiberglass. In view of the translation of all of the wave energy, in certain conditions the passengers and driver on the boat may experience an unpleasant boat ride.
As an alternative to fiberglass, various industries having also looked to the use of polyurethanes. Products utilizing polyurethanes include, but are not limited to, camper tops and coolers. In one process utilizing polyurethanes, a shell member constituting inner and outer skins is formed by conventional methods such as thermoforming. To provide for insulation and rigidity, a foaming process is performed wherein the polyurethane material is injected or disposed between the skins. However, under pressure the injected foam expands. As the outer and inner skins are not strong enough to resist the expanding foam, foam fixtures are provided to keep the skins in place and, thus, to prevent the skins from blowing out. Other methods used with polyurethane include the rotomold method and the twin sheet thermoforming method.
U.S. Pat. No. 4,910,067 issued to O""Neill discloses a thermoplastic/foam core/fiber-reinforced resin structural composite material. This composite structure consists of a thermoplastic layer, a layer of fibrous material spaced from the thermoplastic layer and a foam core disposed in the space between the layers. A resin impregnates and holds the layer of fibrous material together to form a fiber-reinforced resin structure. The thermoplastic layer consists of an acrylic ABS and utilizes a foamable urethane resin as its core material. In manufacturing the acrylic ABS layer is vacuumformed to its intended shape. The urethane foam is manufactured through injecting molding techniques.
As seen from the above description the forming processes required when utilizing polyurethane or urethanes are relatively involved and costly. In at least some of the above describe processes no bonding of the foam core to the outer skins occurs. Furthermore, the end product constructed from polyurethane have several drawbacks as they are normally less durable and are normally not recyclable. Furthermore, polyurethanes are known to contain a great deal of toxicity.
Thus what is needed in the art is a composite material which can be utilized to replace or be substituted for fiberglass or other materials such as polyurethanes during the manufacture of products normally containing fiberglass or the other materials as a primary component. It is, therefore, to the effective resolution of the aforementioned problems and shortcomings that the present invention is directed.
The present invention provides for a thermoplastic multi-layer composite structure consisting in a first embodiment of a co-extruded acrylic polypropylene outer skin and high melt strength polypropylene substrate which is attached to a first surface of a polypropylene foam core. An inner polypropylene skin can be attached to a second surface of the foam core.
Polypropylene is a member of a family of plastics called olefins and is a crystalline structure. The high density polypropylene provides for a relatively hard and stiff surface. The polypropylene also provides for a high degree of recyclability.
The foam core can either be constructed from an expanded polypropylene or an extruded polypropylene. Where an expanded polypropylene foam core is provided, the foam core is attached to the outer and inner skin through the use of a polypropylene adhesive.
Where the extruded polypropylene foam core is provided, the skins can be attached to the foam core through a welding or bonding process in lieu of adhesives. However, it should be understood that the polypropylene adhesives can also be utilized for attaching the skins to the extruded foam core. Additionally, the extruded foam core can vary in density to provide a composite foam core. In construction, the density of the foam core is determined by the amount of air entrapped. The more expanded the cells of the core are, the lower the density of the polypropylene foam. To construct a composite polypropylene foam core of varying density, the various density foams are fused or bonded together, similar to the fusing of the extruded foam core to the outer and inner skins.
Preferably, the various densities of the composite foam core are arranged such that the lowest density foam is provided at the center of the core and the varying densities of the foam core extend outward from the center in numerical order (i.e. lowest density at center of foam core, highest density at outer surface of foam core).
Accordingly, it is an object of the present invention to provide a thermoplastic multi-layer composite structure which can replace fiberglass, composite structures containing polyurethane or similar structures for certain applications.
It is another object of the present invention to provide a thermoplastic multi-layer composite structure which provides superior impact strength as compared to fiberglass, composite structures containing polyurethane or similar structures.
It is still another object of the present invention to provide a thermoplastic multi-layer composite structure which is relatively cheaper in cost to construct as compared to fiberglass, composite structures containing polyurethane or similar structures.
It is even still another object of the present invention to provide a thermoplastic multi-layer composite structure which is generally one hundred (100%) percent recyclable.
It is yet another object of the present invention to provide a thermoplastic multi-layer composite structure which will absorb a relatively higher amount energy as compared to fiberglass, wood, composite structures containing polyurethane or similar structures.
It is yet still another object of the present invention to provide a thermoplastic multi-layer composite structure which requires less maintenance as compared to fiberglass, composite structures containing polyurethane or similar structures.
It is a further object of the present invention to provide a thermoplastic multi-layer composite structure which does not contain toxic materials.
In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.